The human host uses complex defense strategies against HIV-1 infection, including humoral and cell mediated immunity. We have identified a novel route of T cell-mediated resistance to HIV-1 infection which forms the basis of the program proposed here. In studies on the function of the HIV-1 vif gene we found that SupT1 cells cocultivated with vif-mutant HIV-1 infected peripheral blood lymphocytes became resistant to subsequent challenge by wildtype (wt) HIV-1. The resistant SupT1 cells, termed R1c, were found to carry HIV-1 cDNA at low levels but did not produce sedimentable virus particles or detectable viral protein. They express surface CD4 and CD4 mRNA at levels comparable to control SupT1, but have barely detectable levels of CXCR4 mRNA encoding a coreceptor required for HIV-1 entry. Naive SupT1 exposed to soluble products of Rlc also downmodulate expression of CXCR4 but not CD4, and acquire resistance to wt HIV-1 challenge. These results indicate that Rlc cells release a soluble factor that can induce resistance to HIV-1 infection in susceptible cells through transcriptional downmodulation of an HIV-1 coreceptor. The investigators propose this research project to examine the molecular basis of this new route of cellular immune response to HIV-1. First they will isolate and characterize Rlc clones demonstrating resistance to HIV-1 infection which produce soluble factors conferring resistance to HIV-1 infection to susceptible cells. Selected resistant and sensitive Rlc clones will be used for isolation of differentially expressed cDNAs by reciprocal subtraction differential RNA display (RSDD). Using an antisense cloning approach the investigators will examine sets of pooled cDNA for the ability to block the production of HIV inhibitory factors in Rlc clones. Active antisense cDNAs will be used to obtain full-length cDNAs encoding factors that confer resistance to HIV-1. Finally, these full-length cDNA(s) will be cloned into an Ecdysone-inducible expression system to confirm the identity of molecules responsible for acquired resistance to HIV-1 in transformed and primary cell lines. These studies will identify new human gene products that mediate cellular resistance to HIV-1.